1. Field of the Invention
The present invention relates to a network such as a LAN (Local Area Network), and more specifically to a network connection circuit which connects a terminal to the network.
2. Description of the Prior Art
There has been used a network connection circuit connecting a terminal to a network. FIG. 10 shows the configuration of a conventional network connection circuit for a LAN, provided in a terminal. As shown in FIG. 10, the LAN connection circuit 1-1 comprises the LAN cable connector 1-10 connected to a LAN via the packet receipt cable 1-12 and the packet transmission cable 1-11, the packet transmission filter 1-20, the packet receipt filter 1-21, the transceiver 1-22 driving the LAN physical layer, the signal line 1-13 laid between the transceiver 1-22 and the packet transmission filter 1-20, the signal line 1-14 laid between the transceiver 122 and the packet receipt filter 1-21, the LAN controller (LANC) 1-23 which controls preparation and analysis of packets, the signal line 1-15 laid between the LAN controller 1-23 and the transceiver 1-22, the signal line 116 laid between the LAN controller 1-23 and the transceiver 1-22, and the signal line 1-17 laid between the transceiver 1-23 and the central control unit 1-24 connected to an upper layer such as an application (software), which controls the LAN controller 1-23 pursuant to the instruction of the upper layer.
The operation of the LAN connection circuit 1-1 during transmitting and receiving packets over the LAN is as follows, wherein the receipt operation will be described first, and the explanation of the transmission operation will follow. In case of receiving packets, the data from the LAN are reshaped, for example, at the receipt filter 1-21; undergo detection of error, are converted into a given level signal, and are descrambled at the transceiver 1-16; and are fed to the LAN controller 1-23. Further, the LAN controller 1-23 compares the destination address of the receipt data with the address of the terminal. If identical, the LAN controller 1-23 transfers the data to the central control unit 1-24.
In case of transmitting packets, the central control unit 1-24 requests the LAN controller 1-23 to transfer the data output from the upper layer. The LAN controller 1-23 prepares transmission of the packets, including insertion of preamble patterns into the header of the packets. The packets experience an electric conversion and a scramble processing at the transceiver 1-22 to reach the LAN via the transmission filer 1-20 and the LAN connector 1-10. The LAN connection circuit 1-1 as described above, serves for constructing a LAN system.
As shown FIG. 11, the LAN system incorporates a plurality of terminals 2-31, the network line concentrator 2-1 (e.g., HUB), and the backbone network 2-21, which forms a star connection as a topology. The LAN terminals 2-31 each have the LAN connection circuit 1-1 as shown in FIG. 10, which execute the transmission and receipt of data using it. Further, all of the LAN terminals 2-31 are connected to the terminal ports 2-11 of the network line concentrator 2-1 via the LAN cables 2-22. Similarly, the backbone network 2-21 is connected to the backbone network port 2-10 of the network line concentrator 2-1 via the LAN cable 2-20. Upon receipt of data in one of the ports 2-11, 2-10, the network line concentrator 2-1 forwards the data to all of the LAN terminals 2-31 or some thereof.
In such a LAN system, however, connecting one LAN terminal 2-31 to the network line concentrator 2-1 requires one port 2-11 thereof. If another LAN terminal 2-31 is added on the LAN system, it is necessary to replace the network line concentrator 2-1 with another network line concentrator which is capable of accommodating more LAN terminals 2-31, or to add another network line concentrator 2-1. Besides, with the star connection, the LAN system needs much time and money to extend the LAN cables 2-22 to the add-on LAN terminal 2-31, and more time and money if they are laid extremely far from the network line concentrator 2-1.